With recent advances in small-incision cataract surgery, increased emphasis has been placed on developing artificial ophthalmic lenses made of soft, pliable polymers whereby the lens can be folded and implanted in the eye through the same incision used to remove the natural lens. One of the primary classes of polymers found to achieve this objective is hydrogels.
Hydrogel materials are rigid when dry but can be hydrated with large amounts of water (generally 20-70% by weight) become soft and pliable. However, the hydration process tends to the refractive index of the hydrated polymer. For example, currently recognized hydrogels have a refractive index that is generally less than about 1.48. In addition to adversely affecting refractive index, the absorbed water also significantly increases the diameter and thickness of the IOLs, for example, by as much as about 15 percent.
U.S. Pat. No. 5,290,892 (Namdaran et al.), U.S. Pat. No. 5,331,073 (Weinschenk, III et al.), and U.S. Pat. No. 5,693,095 (Freeman et al.), each of which is incorporated by reference as if fully set forth herein, discuss forming foldable lenses from ethoxyaryl (meth)acrylate with a crosslinker or with a second acrylate monomer and crosslinker. The resulting polymer is soft and foldable and the patents further discuss mold-forming the polymer into lenses. U.S. Pat. No. 5,433,746 to Namdaran et al., which is also incorporated by reference as if fully set forth herein, discloses forming flexible intraocular lenses by molding polymeric materials which have a relatively low glass transition temperature. Such molding requires specialized equipment and expensive customized molds. In addition, the resulting molded lenses tend to have poor surface quality since they generally cannot be polished. To ameliorate this problem U.S. Pat. No. 5,331,073 discusses forming lenses from a soft/foldable material by machining the lenses at cryogenic temperatures, a cumbersome and expensive process.
What is needed is a polymer that in its unhydrated state can be machined using conventional technology and in its hydrated state is soft, foldable and has a high refractive index. The current invention provides such a polymer and a method of manufacturing a foldable IOL from it.